Cold start engine exhaust emissions is a key component for overall vehicle emission control. During the cold start, it may be difficult to achieve full combustion during the crank and run up on an engine and still maintain the minimum emission requirements. Specifically, direct injection gasoline engines may have several unique issues during starting, such as larger variation in injection rail pressure and/or more limited air and fuel mixing. Further, unlike port injection, most all of the fuel injected is present in the cylinder, and therefore if not combusted it may leave the engine as unburnt hydrocarbons.
The above issues may be exacerbated by the rapid changes in cylinder conditions during the engine starting/cranking/run-up process. For example, cylinder charge motion, fuel-air mixing, residual gas amounts, residual temperatures, cylinder temperatures, etc., can rapidly change from one combustion event to the next.
The inventors herein have recognized that the number and/or timing of injections during the engine staring process can also result in large variation in cylinder conditions, such as mixing, etc., and thus when correlated with the cylinder combustion event number from a first combustion, for example, may be varied in selected ways to achieve improved combustion over a greater range of events in a more repeatable fashion.
In one particular example, improved starting may be achieved by a method for starting an internal combustion engine having direct fuel injection, comprising adjusting a number of direct injections per combustion cycle based on a cylinder event number from a first cylinder event.
Of course, various alternatives may also be used, such as those described herein.